This invention relates to the repair of gas turbine engine components and, more particularly, to a method for depositing material to increase the thickness of load-bearing components in gas turbine engines, including honeycomb backing material such as in compressor discharge pressure (CDP) seals, forward inner nozzle supports, aft seals, and others.
The honeycomb in aircraft engine seals is replaced essentially every time an engine is torn down to permit re-grinding the diameters to restore seal clearances and aid in engine efficiency retention. The honeycomb is removed by a variety of methods, including air hammer chiseling, machining, grinding, chemical etching, and other methods. The honeycomb backing is typically thin, on the order of less than about 0.1 inch (0.25 cm), and often becomes distorted due to stresses encountered in service. Honeycomb removal, no matter how carefully conducted, gradually thins the backing as the honeycomb is removed multiple times during multiple repairs. Eventually, the backing is too thin to be serviceable, rendering the entire component scrap. While backing thinned to about 20% below the new part minimum thickness is acceptable for service, backing thinned further is not acceptable for service, as increased service stresses tend to cause cracking. Typical backing materials are IN718, IN625, Hastelloy X, Renxc3xa9 41, Waspaloy, IN903, IN907, IN909, and others. There has been a need for a cost effective, low distortion process for rebuilding material thickness on backings which yields acceptable mechanical properties in the build up material as well as in the joint between the build up material and the substrate, to permit salvage of scrapped or otherwise unuseable components.
Conventional salvage methods to add thickness to backing, such as welding, generally produce excessive distortion because the backing is thin. Such welding processes can produce acceptable bond strengths and added material strengths, but have not been successful to date because of distortion. Low heat input TIG welding and laser welding have been attempted, but excessive distortion remains a problem. Conventional thermal sprays can restore the backing thickness, but bond strength and added material strength is too low, typically on the order of only 10% of the backing material strength. This characteristic effectively limits use of conventional thermal spray to applications in compression.
A high velocity oxy-fuel (HVOF) process has been developed to apply CoNiCrAlY material to the flow path of relatively non load-bearing investment cast Ni-based (such as IN738) and Co-based (such as MarM509) turbine shrouds, such as high pressure turbine (HPT) shrouds. In such shrouds the segment length is short, in-service bending is low, resistance to hot gas corrosion and resistance to high temperatures are required, and mechanical strength and grain growth are not issues. In connection with this process for turbine shrouds, adequate bond strengths have been achieved by the use of a high temperature diffusion.
Briefly, therefore, the invention is directed to a method for restoring thickness of gas turbine engine components such as seals having honeycomb structure on a backing substrate, flanges or casing pockets. A build-up material is deposited onto the backing substrate by a method selected from high velocity oxy-fuel deposition and low pressure plasma spray deposition.
The invention is also directed to a method for repairing a gas turbine engine component comprising a honeycomb structure on a backing substrate. Honeycomb structure is removed from the backing substrate; the backing substrate is roughened and cleaned. A selected build-up material is deposited onto the backing substrate by a method selected from high velocity oxy-fuel deposition and low pressure plasma spray. The backing substrate is heat treated to diffuse deposited build-up material into the substrate, enhance bond strength between deposited build-up material and the substrate, and enhance the bond strength between build-up material particles.
In another aspect, the invention is a method for repairing a gas turbine engine component comprising honeycomb structure on a backing substrate. Honeycomb structure is removed from the backing substrate. A build-up material comprising from about 4 to about 8 wt % Al, from about 15 to about 22 wt % Cr, and balance Ni is deposited onto the backing substrate by a method selected from high velocity oxy-fuel deposition and low pressure plasma spray. The substrate is heat treated to diffuse deposited build-up material into the substrate, enhance bond strength between deposited build-up material and the substrate, and enhance the bond strength between build-up material particles.
The invention is further directed to a method for repairing a gas turbine engine component comprising honeycomb structure on a backing substrate in which a build-up material is deposited onto the substrate by high velocity oxy-fuel deposition employing a fuel-to-oxygen ratio which produces a reducing deposition atmosphere thereby reducing oxidation of build-up material during deposition.
The invention is further directed to a method for restoring thickness to a load-bearing gas turbine engine component. A surface of the component is mechanically roughened to produce a roughened surface. The roughened surface is cleaned to remove residue remaining from the mechanical roughening. A build-up material is deposited onto the roughened surface by a method selected from high velocity oxy-fuel deposition and low pressure plasma spray. The backing substrate is heat treated to diffuse deposited build-up material into the substrate, enhance bond strength between deposited build-up material and the substrate, and enhance the bond strength between build-up material particles.
Other objects and other features will be in part apparent and in part pointed out hereinafter.